[RMVX ACE] HOW TO ADD BORDERS TO BATTLE LOG?

class Window_BattleLog < Window_Selectable
  def initialize
    super(0, 0, window_width, window_height)
    self.z = 200
    self.opacity = 0
    @lines = []
    @num_wait = 0
    #create_back_bitmap
    #create_back_sprite
    refresh
  end

  def update_tone
    self.tone.set(0,0,0)
  end
  
  def dispose
    super
    #dispose_back_bitmap
    #dispose_back_sprite
  end
  
  def refresh
    if @lines.size > 0
      height = line_number * line_height + padding * 2
      move(0,0,window_width,height)
      self.opacity = 255
    else
      self.opacity = 0
    end
    contents.clear
    @lines.size.times {|i| draw_line(i) }
  end
end